Abstract [en]

In Drosophila melanogaster, eyeless and twin of eyeless have important function during eye development. Mutants of both genes give a variety of eye and head phenotypes with the strongest being almost headless meaning that they lack all structures derived from the eye-antennal disc. toy the first eye specification gene expressed in the regulatory network that leads to eye formation and the gene actvates eyeless. What regulates toy is still not clear and has been the focus of this thesis. In Paper I, we analysed part of the upstream region of the toy gene to be able to drive reporter genes with the expected expression pattern in embyo and larval tissues. We found that a 1300-bp region surrounding the toy transcription start is important for correct Toy expression during embryonic and larval development. We also tested for possible redundancy between the toy and ey genes by rescue experiments on some lethal allels in both genes and found that Pax-6 proteins can substitute for each other concerning both head structures and survival. However, rescue is only partial, indicating that the proteins are not fully compatible or that the levels of expression are not sufficiently reproduced by the artificial Gal4-UAS system. Furthermore, we show that inhibition of apoptosis increased survival in strong toy mutants, but did not improve eye phenotypes. In Paper II, we searched for possibly upstream regulators of toy and found that the head gap gene empty spiracles changed the expression pattern of Toy significantly in the embryonic eye-antennal primordium. By clonal analysis and ectopic expressions, we made the conclusion that Ems acts as a repressor of toy during late embryonic development and also at later developmental stages. In Paper III, we investigate presumptive toy enhancer regions within the intron sequences of the gene. Generation and examination of transgenic lines showed that there might be an enhancer region driving toy expression in the embryonic ventral nerve cord within intron 2.

Abstract [en]

There are two Pax6 genes in Drosophila melanogaster; eyeless (ey) and twin-of-eyeless (toy), due to a duplication, which most likely occurred in the insect lineage. They encode transcription factors important for head development. Misexpression of either toy or ey can induce formation of ectopic compound eyes. Toy regulates the ey gene by binding to an eye-specific enhancer in its second intron. However, Toy can induce ectopic eyes also in an ey( - ) background, which indicates a redundancy between the two Pax6 copies in eye formation. To elucidate to what extent these two genes are interchangeable, we first generated toy-Gal4 constructs capable of driving the Pax6 genes in a toy-specific manner. Genetic dissection of the promoter proximal region of toy identified a 1,300-bp region around the canonical transcription start that is sufficient to drive toy expression in embryonic brain and eye primorida and in larval eye-antennal discs. We find that exogenous expression of toy can partially rescue the lethality and eye phenotype caused by lethal mutations in ey and vice versa. We therefore conclude that Toy and Ey, to some extent, can substitute for each other. Nevertheless, the phenotypes of the rescued flies indicate that the two Pax6 genes are specialized to regulate defined structures of the fly head.

Jacobsson, Linn

Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).

Skottheim Honn, John

Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).

Ekström, Karin

Rasmuson-Lestander, Åsa

Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).

(English)Manuscript (preprint) (Other academic)

Abstract [en]

The specification of the eye-antennal disc primordium in the Drosophila embryo requires the expression of two paralogous Pax6 genes: twin of eyeless (toy) and eyeless (ey). toy is considered to be the first eye specification gene expressed in the regulatory network that governs eye formation and the gene that, in turn, activates eyeless. What regulates toy expression is, however, still unclear. We show, by misexpression and mutant analysis, that the head-specific gene empty spiracles alters the expression pattern of Toy in the head region around the visual primordia.

Jacobsson, Linn

Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).

Rasmuson-Lestander, Åsa

Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).

(English)Manuscript (preprint) (Other academic)

Abstract [en]

In Drosophila there are two paralougus Pax-6 genes, twin of eyeless (toy) and eyeless (ey) Both genes have an extensive elaborate expression pattern in the brain and ventral nerve cord but are not activated at the same time in these regions. Since both genes are expressed in several tissues during different time points in development, one might expect that more than one regulatory enhancer controls them. It is known, that eyeless is directly regulated by toy at the beginning of eye development and it has been shown that there are binding sites for regulatory proteins within the introns of the eyeless gene and in vertebrate Pax-6 genes. We investigate the transcriptional activation of toy within the intron sequences of the gene and show that there is a presumptive regulatory element in intron 2, controlling toy expression in the ventral nerve cord of embryos.